Inductor devices – Winding with terminals – taps – or coil conductor end...
Reexamination Certificate
1999-05-24
2003-04-22
Nguyen, Tuyen T. (Department: 2832)
Inductor devices
Winding with terminals, taps, or coil conductor end...
C336S083000, C336S200000
Reexamination Certificate
active
06552642
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic device having electric wires such as a wire-wound chip coil and to a method of producing such a coil device. The present invention also relates to a method of producing an electronic device having electric wires in an inductance component. More particularly, the present invention relates to a method of producing an electronic device having electric wires including an improved process of connecting end portions of an insulated electric wire wound around a core to electrodes located on the core.
2. Description of the Related Art
FIG. 5
illustrates a conventional chip coil made up of an electric wire
5
wound around a core
1
made of a magnetic material, wherein ends
5
a
of the wire
5
are connected, via thermo-compression bonding such as a wire bonding process, to respective electrodes
2
located on the core
1
. The electrodes
2
are made of a material such as Ag or Ag—Pd. When the ends
5
a
of the wire are connected to the respective electrodes
2
, the resultant connecting portions of the wire
5
have raised portions bulging from the surface of the electrodes
2
. The bulging shape of the connecting portions causes the chip coil to become unstable when it is mounted on a printed circuit board. That is, the chip coil is mounted unevenly in a slanted orientation or topples over and is separated from the printed circuit board in the worst case. Another problem with the chip coil of this type is that the ends
5
a
of the wire
5
are exposed directly to air and thus, the ends of the wire are oxidized. This makes it difficult to solder the ends of the wire during the process of mounting the chip coil.
One possible technique of improving the stability of the mounted position is to form recesses
3
as seen in
FIG. 6
in both end portions of the core
1
so that the ends
5
a
of the wire can be placed inside the recesses
3
. However, the shape of the core
1
becomes complicated and difficult processes are required to produce such a complicated structure including the recesses
3
.
The insulated electric wire
5
generally consists of an electric wire made of metal such as copper whose outer surface is coated with an insulating material such as polyesterimide. The insulated electric wire is connected to the electrodes via, for example, pulse heating. The connection process via pulse heating is described below with reference to FIG.
11
.
In
FIG. 11
, cross sections of the core
51
of the coil device and the electrode
52
located on the upper surface of the core
51
are shown. An end portion of the insulated electric wire
53
is disposed on the electrode
52
.
A pressing tip
56
heated at about 500° C. is moved down so that the insulated electric wire
53
is pressed against the electrode
52
. The electric wire
53
a
is flattened by the pressure and the electric wire
53
a
is connected to the electrode
52
via thermo-compression bonding.
In this connection technique, if the electrode
52
is made of metal having a high melting point such as Ag, Cu, or Ni, the insulating coating
53
b
melts at a temperature lower than the melting point of the electrode
52
, and the electric wire
53
a
and the electrode
52
are directly connected to each other. Another feature of this technique is that the electric wire
53
a
is flattened by the pressure.
However, although the electric wire
53
a
on the electrode
52
is flattened, there is still a processing step required on the surface of the electrode
52
and the electric wire
53
a.
When the coil device is mounted on a printed circuit board such that the surface of the electrode
52
and attached electric wire
53
a
comes into contact with the printed circuit board, the above-described step can cause the coil device to become unstable or cause the soldered connection to become unreliable.
In many cases, the surface of the electrodes
52
of the coil device is plated with metal having a low melting point such as Sn or solder so that a low-melting-point electrode layer is formed on the electrode
52
thereby ensuring that the electrode can be easily soldered. For example, as shown in
FIG. 12
, the electrode
52
is produced by coating a silver-filled paste on the surface of the core
51
and baking it so as to form a base layer
52
a,
then plating the surface of the base layer
52
a
with Ni thereby forming a Ni-plated layer
52
b
for protecting the base layer
52
a
from being eroded by solder, and finally forming an electrode layer
52
c
of low-melting-point metal which allows the electrode
52
to be easily soldered.
In the case of the coil device having the above structure, when connection is performed with the pressing tip
54
heated at about 500° C., the electrode layer
52
c
is heated by the pressing tip
54
to a temperature higher than the melting point of the low-melting-point metal. In the connecting process, the electrically conductive wire
53
a
is pressed by a pressure high enough to compress the electrically conductive wire
53
a.
As a result, the insulating coating
53
b
and the electrode layer
52
c
made of the low-melting-point metal at the top layer are both melted into liquid states, and the electrically conductive wire
53
a
is compressed into a flattened shape.
As a result, in the pressing process using the pressing tip
54
, the low-melting-point metal in the liquid state is pushed aside by the insulating coating
53
b
in the liquid state toward the sides of the electrically conductive wire
53
a.
In the above process, after the low-melting-point metal is pushed aside by the melted insulating coating
53
b,
if the melted insulating coating
53
b
sticks to the pressing tip
54
and is removed when the pressing tip
54
is moved up to its original position, the Ni-plated layer
52
b
is sometimes exposed in an area A at a side of the conductive wire
53
a.
If the Ni-plated layer
52
b
is partially exposed, when the coil device is mounted on a printed circuit board via soldering, a connection failure can occur because the Ni-plated layer
52
b
has poor solder wettability.
Even in the case where the Ni-plated layer
52
b
does not become exposed in the area A in
FIG. 12
after the low-melting-point metal is pushed aside by the melted insulating coating
53
b,
if the melted insulating coating
53
b
sticks to the pressing tip
54
and is removed when the pressing tip
54
is moved up to its original position, a crater
52
d
is produced in an area on the surface of the electrode
52
where the insulating coating
53
b
of the electrically conductive wire
53
a
was present. If such a crater is produced, it becomes difficult to make a good connection in the soldering process.
SUMMARY OF THE INVENTION
To overcome the problems described above, preferred embodiments of the present invention provide an electronic device including a wire which is mounted in a stable fashion, firmly connected to an electrode and is very resistant to oxidization and a method of producing such an electronic device.
In addition, preferred embodiments of the present invention provide a method of producing a coil device, capable of connecting an insulated electric wire to an electrode for connection to an outer circuit in such a manner that the insulated electric wire is embedded in the electrode thereby ensuring that the coil device can be connected to the outer circuit in a highly reliable fashion without causing a soldering failure or any problem which occurs in the conventional techniques.
According to a preferred embodiment of the present invention, an electronic device includes an electric wire firmly connected to an electrode located on an insulating base, the electrode including at least a solder barrier layer made of a material with a high melting point and an easy-soldering layer made of a material with a low melting point; and the electric wire is embedded via a thermo-compression process in the easy-soldering layer in such a manner that the resultant structure has a substantially flat surface.
In
Bando Masahiro
Hatakenaka Tetsuo
Hirotsuji Takayuki
Kasahara Kazuo
Morinaga Tetsuya
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
Nguyen Tuyen T.
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